Thai authorities have declared a state of emergency amid ongoing anti-government protests.
Riot police moved to clear out demonstrators shortly after the announcement.
Officials said they arrested 22 people, including several top leaders of the student-led protest movement.
Protesters are calling for new elections and democratic reforms to the constitutional monarchy. The monarchy, though, is widely considered a pillar of Thai society and criticism of it is a punishable offense.
The emergency decree comes one day after demonstrators heckled a royal motorcade.